During performance tests in 2005 and 2006, Perham violated the emission standards for mercury (Hg) and hydrogen chloride (HCl). Perham uses activated carbon to collect Hg from the stack gases and lime to collect HCl. EPA believes that Perham violated the emission standards because the feed rates of mercury and chlorine compounds were higher than normal on the days on which Perham conducted stack tests. (The Small Municipal Waste Combustor Federal Plan does not require Perham to measure or limit the Hg or chlorine feed rates.) Perham had complied with the Hg and HC standards at the same adsorbent feed rate for each pollutant in other stack tests. The SEP consists of two improvements that will improve their collection efficiency of Hg and HCl. Perham did not know and did not estimate the improved efficiency. The case engineer assumed that the improvements will reduce the previous average emission concentrations of Hg and HCl by 50%.